The present invention relates to a method for making siloxane copolycarbonates. More particularly, the present invention relates to a melt condensation polymerization method for making siloxane copolycarbonates.
Siloxane copolycarbonates and methods for their production have been studied extensively throughout the years. Siloxane copolycarbonates are well known thermoplastic resins which have good flow and mold release characteristics in injection molding applications. The synthetic method commonly used to make siloxane copolycarbonates is an interfacial phosgenation process.
The interfacial phosgenation process, as described by Phelps et al. in U.S. Pat. No. 5,530,083, involves reacting an aromatic dihydroxy compound, phosgene and catalyst with a hydroxyaryl terminated diorganopolysiloxane. This method successfully integrates siloxane monomers into copolycarbonates. Unfortunately, the interfacial phosgenation process uses chemically hazardous phosgene and an environmentally hazardous chlorinated solvent.
Melt condensation polymerization is a well known process for the production of polymers such as copolycarbonates. This method has yet to be utilized to produce siloxane copolycarbonates. During the typical melt process, severe decomposition of the siloxane chain occurs via siloxane chain scission followed by siloxane depolymerization to give cyclic siloxanes such as dimethylsiloxane cyclic tetramer (D.sub.4). The degradation of the siloxane chain inhibits the production of siloxane copolycarbonates and thus, this method is not utilized to produce siloxane copolycarbonates.
Due to environmental concerns with the interfacial method and the degradation of the siloxane chain with the melt condensation polymerization method, new methods of synthesizing siloxane copolycarbonates are constantly being sought.